linux/fs/locks.c

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/*
* linux/fs/locks.c
*
* Provide support for fcntl()'s F_GETLK, F_SETLK, and F_SETLKW calls.
* Doug Evans (dje@spiff.uucp), August 07, 1992
*
* Deadlock detection added.
* FIXME: one thing isn't handled yet:
* - mandatory locks (requires lots of changes elsewhere)
* Kelly Carmichael (kelly@[142.24.8.65]), September 17, 1994.
*
* Miscellaneous edits, and a total rewrite of posix_lock_file() code.
* Kai Petzke (wpp@marie.physik.tu-berlin.de), 1994
*
* Converted file_lock_table to a linked list from an array, which eliminates
* the limits on how many active file locks are open.
* Chad Page (pageone@netcom.com), November 27, 1994
*
* Removed dependency on file descriptors. dup()'ed file descriptors now
* get the same locks as the original file descriptors, and a close() on
* any file descriptor removes ALL the locks on the file for the current
* process. Since locks still depend on the process id, locks are inherited
* after an exec() but not after a fork(). This agrees with POSIX, and both
* BSD and SVR4 practice.
* Andy Walker (andy@lysaker.kvaerner.no), February 14, 1995
*
* Scrapped free list which is redundant now that we allocate locks
* dynamically with kmalloc()/kfree().
* Andy Walker (andy@lysaker.kvaerner.no), February 21, 1995
*
* Implemented two lock personalities - FL_FLOCK and FL_POSIX.
*
* FL_POSIX locks are created with calls to fcntl() and lockf() through the
* fcntl() system call. They have the semantics described above.
*
* FL_FLOCK locks are created with calls to flock(), through the flock()
* system call, which is new. Old C libraries implement flock() via fcntl()
* and will continue to use the old, broken implementation.
*
* FL_FLOCK locks follow the 4.4 BSD flock() semantics. They are associated
* with a file pointer (filp). As a result they can be shared by a parent
* process and its children after a fork(). They are removed when the last
* file descriptor referring to the file pointer is closed (unless explicitly
* unlocked).
*
* FL_FLOCK locks never deadlock, an existing lock is always removed before
* upgrading from shared to exclusive (or vice versa). When this happens
* any processes blocked by the current lock are woken up and allowed to
* run before the new lock is applied.
* Andy Walker (andy@lysaker.kvaerner.no), June 09, 1995
*
* Removed some race conditions in flock_lock_file(), marked other possible
* races. Just grep for FIXME to see them.
* Dmitry Gorodchanin (pgmdsg@ibi.com), February 09, 1996.
*
* Addressed Dmitry's concerns. Deadlock checking no longer recursive.
* Lock allocation changed to GFP_ATOMIC as we can't afford to sleep
* once we've checked for blocking and deadlocking.
* Andy Walker (andy@lysaker.kvaerner.no), April 03, 1996.
*
* Initial implementation of mandatory locks. SunOS turned out to be
* a rotten model, so I implemented the "obvious" semantics.
* See 'Documentation/mandatory.txt' for details.
* Andy Walker (andy@lysaker.kvaerner.no), April 06, 1996.
*
* Don't allow mandatory locks on mmap()'ed files. Added simple functions to
* check if a file has mandatory locks, used by mmap(), open() and creat() to
* see if system call should be rejected. Ref. HP-UX/SunOS/Solaris Reference
* Manual, Section 2.
* Andy Walker (andy@lysaker.kvaerner.no), April 09, 1996.
*
* Tidied up block list handling. Added '/proc/locks' interface.
* Andy Walker (andy@lysaker.kvaerner.no), April 24, 1996.
*
* Fixed deadlock condition for pathological code that mixes calls to
* flock() and fcntl().
* Andy Walker (andy@lysaker.kvaerner.no), April 29, 1996.
*
* Allow only one type of locking scheme (FL_POSIX or FL_FLOCK) to be in use
* for a given file at a time. Changed the CONFIG_LOCK_MANDATORY scheme to
* guarantee sensible behaviour in the case where file system modules might
* be compiled with different options than the kernel itself.
* Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
*
* Added a couple of missing wake_up() calls. Thanks to Thomas Meckel
* (Thomas.Meckel@mni.fh-giessen.de) for spotting this.
* Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
*
* Changed FL_POSIX locks to use the block list in the same way as FL_FLOCK
* locks. Changed process synchronisation to avoid dereferencing locks that
* have already been freed.
* Andy Walker (andy@lysaker.kvaerner.no), Sep 21, 1996.
*
* Made the block list a circular list to minimise searching in the list.
* Andy Walker (andy@lysaker.kvaerner.no), Sep 25, 1996.
*
* Made mandatory locking a mount option. Default is not to allow mandatory
* locking.
* Andy Walker (andy@lysaker.kvaerner.no), Oct 04, 1996.
*
* Some adaptations for NFS support.
* Olaf Kirch (okir@monad.swb.de), Dec 1996,
*
* Fixed /proc/locks interface so that we can't overrun the buffer we are handed.
* Andy Walker (andy@lysaker.kvaerner.no), May 12, 1997.
*
* Use slab allocator instead of kmalloc/kfree.
* Use generic list implementation from <linux/list.h>.
* Sped up posix_locks_deadlock by only considering blocked locks.
* Matthew Wilcox <willy@debian.org>, March, 2000.
*
* Leases and LOCK_MAND
* Matthew Wilcox <willy@debian.org>, June, 2000.
* Stephen Rothwell <sfr@canb.auug.org.au>, June, 2000.
*/
#include <linux/capability.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/security.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/syscalls.h>
#include <linux/time.h>
#include <linux/rcupdate.h>
#include <asm/semaphore.h>
#include <asm/uaccess.h>
#define IS_POSIX(fl) (fl->fl_flags & FL_POSIX)
#define IS_FLOCK(fl) (fl->fl_flags & FL_FLOCK)
#define IS_LEASE(fl) (fl->fl_flags & FL_LEASE)
int leases_enable = 1;
int lease_break_time = 45;
#define for_each_lock(inode, lockp) \
for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)
LIST_HEAD(file_lock_list);
EXPORT_SYMBOL(file_lock_list);
static LIST_HEAD(blocked_list);
static kmem_cache_t *filelock_cache;
/* Allocate an empty lock structure. */
static struct file_lock *locks_alloc_lock(void)
{
return kmem_cache_alloc(filelock_cache, SLAB_KERNEL);
}
/* Free a lock which is not in use. */
static inline void locks_free_lock(struct file_lock *fl)
{
if (fl == NULL) {
BUG();
return;
}
if (waitqueue_active(&fl->fl_wait))
panic("Attempting to free lock with active wait queue");
if (!list_empty(&fl->fl_block))
panic("Attempting to free lock with active block list");
if (!list_empty(&fl->fl_link))
panic("Attempting to free lock on active lock list");
if (fl->fl_ops) {
if (fl->fl_ops->fl_release_private)
fl->fl_ops->fl_release_private(fl);
fl->fl_ops = NULL;
}
if (fl->fl_lmops) {
if (fl->fl_lmops->fl_release_private)
fl->fl_lmops->fl_release_private(fl);
fl->fl_lmops = NULL;
}
kmem_cache_free(filelock_cache, fl);
}
void locks_init_lock(struct file_lock *fl)
{
INIT_LIST_HEAD(&fl->fl_link);
INIT_LIST_HEAD(&fl->fl_block);
init_waitqueue_head(&fl->fl_wait);
fl->fl_next = NULL;
fl->fl_fasync = NULL;
fl->fl_owner = NULL;
fl->fl_pid = 0;
fl->fl_file = NULL;
fl->fl_flags = 0;
fl->fl_type = 0;
fl->fl_start = fl->fl_end = 0;
fl->fl_ops = NULL;
fl->fl_lmops = NULL;
}
EXPORT_SYMBOL(locks_init_lock);
/*
* Initialises the fields of the file lock which are invariant for
* free file_locks.
*/
static void init_once(void *foo, kmem_cache_t *cache, unsigned long flags)
{
struct file_lock *lock = (struct file_lock *) foo;
if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) !=
SLAB_CTOR_CONSTRUCTOR)
return;
locks_init_lock(lock);
}
/*
* Initialize a new lock from an existing file_lock structure.
*/
void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
{
new->fl_owner = fl->fl_owner;
new->fl_pid = fl->fl_pid;
new->fl_file = fl->fl_file;
new->fl_flags = fl->fl_flags;
new->fl_type = fl->fl_type;
new->fl_start = fl->fl_start;
new->fl_end = fl->fl_end;
new->fl_ops = fl->fl_ops;
new->fl_lmops = fl->fl_lmops;
if (fl->fl_ops && fl->fl_ops->fl_copy_lock)
fl->fl_ops->fl_copy_lock(new, fl);
if (fl->fl_lmops && fl->fl_lmops->fl_copy_lock)
fl->fl_lmops->fl_copy_lock(new, fl);
}
EXPORT_SYMBOL(locks_copy_lock);
static inline int flock_translate_cmd(int cmd) {
if (cmd & LOCK_MAND)
return cmd & (LOCK_MAND | LOCK_RW);
switch (cmd) {
case LOCK_SH:
return F_RDLCK;
case LOCK_EX:
return F_WRLCK;
case LOCK_UN:
return F_UNLCK;
}
return -EINVAL;
}
/* Fill in a file_lock structure with an appropriate FLOCK lock. */
static int flock_make_lock(struct file *filp, struct file_lock **lock,
unsigned int cmd)
{
struct file_lock *fl;
int type = flock_translate_cmd(cmd);
if (type < 0)
return type;
fl = locks_alloc_lock();
if (fl == NULL)
return -ENOMEM;
fl->fl_file = filp;
fl->fl_pid = current->tgid;
fl->fl_flags = FL_FLOCK;
fl->fl_type = type;
fl->fl_end = OFFSET_MAX;
*lock = fl;
return 0;
}
static int assign_type(struct file_lock *fl, int type)
{
switch (type) {
case F_RDLCK:
case F_WRLCK:
case F_UNLCK:
fl->fl_type = type;
break;
default:
return -EINVAL;
}
return 0;
}
/* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
* style lock.
*/
static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
struct flock *l)
{
off_t start, end;
switch (l->l_whence) {
case 0: /*SEEK_SET*/
start = 0;
break;
case 1: /*SEEK_CUR*/
start = filp->f_pos;
break;
case 2: /*SEEK_END*/
start = i_size_read(filp->f_dentry->d_inode);
break;
default:
return -EINVAL;
}
/* POSIX-1996 leaves the case l->l_len < 0 undefined;
POSIX-2001 defines it. */
start += l->l_start;
end = start + l->l_len - 1;
if (l->l_len < 0) {
end = start - 1;
start += l->l_len;
}
if (start < 0)
return -EINVAL;
if (l->l_len > 0 && end < 0)
return -EOVERFLOW;
fl->fl_start = start; /* we record the absolute position */
fl->fl_end = end;
if (l->l_len == 0)
fl->fl_end = OFFSET_MAX;
fl->fl_owner = current->files;
fl->fl_pid = current->tgid;
fl->fl_file = filp;
fl->fl_flags = FL_POSIX;
fl->fl_ops = NULL;
fl->fl_lmops = NULL;
return assign_type(fl, l->l_type);
}
#if BITS_PER_LONG == 32
static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
struct flock64 *l)
{
loff_t start;
switch (l->l_whence) {
case 0: /*SEEK_SET*/
start = 0;
break;
case 1: /*SEEK_CUR*/
start = filp->f_pos;
break;
case 2: /*SEEK_END*/
start = i_size_read(filp->f_dentry->d_inode);
break;
default:
return -EINVAL;
}
if (((start += l->l_start) < 0) || (l->l_len < 0))
return -EINVAL;
fl->fl_end = start + l->l_len - 1;
if (l->l_len > 0 && fl->fl_end < 0)
return -EOVERFLOW;
fl->fl_start = start; /* we record the absolute position */
if (l->l_len == 0)
fl->fl_end = OFFSET_MAX;
fl->fl_owner = current->files;
fl->fl_pid = current->tgid;
fl->fl_file = filp;
fl->fl_flags = FL_POSIX;
fl->fl_ops = NULL;
fl->fl_lmops = NULL;
switch (l->l_type) {
case F_RDLCK:
case F_WRLCK:
case F_UNLCK:
fl->fl_type = l->l_type;
break;
default:
return -EINVAL;
}
return (0);
}
#endif
/* default lease lock manager operations */
static void lease_break_callback(struct file_lock *fl)
{
kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
}
static void lease_release_private_callback(struct file_lock *fl)
{
if (!fl->fl_file)
return;
f_delown(fl->fl_file);
fl->fl_file->f_owner.signum = 0;
}
static int lease_mylease_callback(struct file_lock *fl, struct file_lock *try)
{
return fl->fl_file == try->fl_file;
}
static struct lock_manager_operations lease_manager_ops = {
.fl_break = lease_break_callback,
.fl_release_private = lease_release_private_callback,
.fl_mylease = lease_mylease_callback,
.fl_change = lease_modify,
};
/*
* Initialize a lease, use the default lock manager operations
*/
static int lease_init(struct file *filp, int type, struct file_lock *fl)
{
fl->fl_owner = current->files;
fl->fl_pid = current->tgid;
fl->fl_file = filp;
fl->fl_flags = FL_LEASE;
if (assign_type(fl, type) != 0) {
locks_free_lock(fl);
return -EINVAL;
}
fl->fl_start = 0;
fl->fl_end = OFFSET_MAX;
fl->fl_ops = NULL;
fl->fl_lmops = &lease_manager_ops;
return 0;
}
/* Allocate a file_lock initialised to this type of lease */
static int lease_alloc(struct file *filp, int type, struct file_lock **flp)
{
struct file_lock *fl = locks_alloc_lock();
int error;
if (fl == NULL)
return -ENOMEM;
error = lease_init(filp, type, fl);
if (error)
return error;
*flp = fl;
return 0;
}
/* Check if two locks overlap each other.
*/
static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
{
return ((fl1->fl_end >= fl2->fl_start) &&
(fl2->fl_end >= fl1->fl_start));
}
/*
* Check whether two locks have the same owner.
*/
static inline int
posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
{
if (fl1->fl_lmops && fl1->fl_lmops->fl_compare_owner)
return fl2->fl_lmops == fl1->fl_lmops &&
fl1->fl_lmops->fl_compare_owner(fl1, fl2);
return fl1->fl_owner == fl2->fl_owner;
}
/* Remove waiter from blocker's block list.
* When blocker ends up pointing to itself then the list is empty.
*/
static inline void __locks_delete_block(struct file_lock *waiter)
{
list_del_init(&waiter->fl_block);
list_del_init(&waiter->fl_link);
waiter->fl_next = NULL;
}
/*
*/
static void locks_delete_block(struct file_lock *waiter)
{
lock_kernel();
__locks_delete_block(waiter);
unlock_kernel();
}
/* Insert waiter into blocker's block list.
* We use a circular list so that processes can be easily woken up in
* the order they blocked. The documentation doesn't require this but
* it seems like the reasonable thing to do.
*/
static void locks_insert_block(struct file_lock *blocker,
struct file_lock *waiter)
{
if (!list_empty(&waiter->fl_block)) {
printk(KERN_ERR "locks_insert_block: removing duplicated lock "
"(pid=%d %Ld-%Ld type=%d)\n", waiter->fl_pid,
waiter->fl_start, waiter->fl_end, waiter->fl_type);
__locks_delete_block(waiter);
}
list_add_tail(&waiter->fl_block, &blocker->fl_block);
waiter->fl_next = blocker;
if (IS_POSIX(blocker))
list_add(&waiter->fl_link, &blocked_list);
}
/* Wake up processes blocked waiting for blocker.
* If told to wait then schedule the processes until the block list
* is empty, otherwise empty the block list ourselves.
*/
static void locks_wake_up_blocks(struct file_lock *blocker)
{
while (!list_empty(&blocker->fl_block)) {
struct file_lock *waiter = list_entry(blocker->fl_block.next,
struct file_lock, fl_block);
__locks_delete_block(waiter);
if (waiter->fl_lmops && waiter->fl_lmops->fl_notify)
waiter->fl_lmops->fl_notify(waiter);
else
wake_up(&waiter->fl_wait);
}
}
/* Insert file lock fl into an inode's lock list at the position indicated
* by pos. At the same time add the lock to the global file lock list.
*/
static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
{
list_add(&fl->fl_link, &file_lock_list);
/* insert into file's list */
fl->fl_next = *pos;
*pos = fl;
if (fl->fl_ops && fl->fl_ops->fl_insert)
fl->fl_ops->fl_insert(fl);
}
/*
* Delete a lock and then free it.
* Wake up processes that are blocked waiting for this lock,
* notify the FS that the lock has been cleared and
* finally free the lock.
*/
static void locks_delete_lock(struct file_lock **thisfl_p)
{
struct file_lock *fl = *thisfl_p;
*thisfl_p = fl->fl_next;
fl->fl_next = NULL;
list_del_init(&fl->fl_link);
fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
if (fl->fl_fasync != NULL) {
printk(KERN_ERR "locks_delete_lock: fasync == %p\n", fl->fl_fasync);
fl->fl_fasync = NULL;
}
if (fl->fl_ops && fl->fl_ops->fl_remove)
fl->fl_ops->fl_remove(fl);
locks_wake_up_blocks(fl);
locks_free_lock(fl);
}
/* Determine if lock sys_fl blocks lock caller_fl. Common functionality
* checks for shared/exclusive status of overlapping locks.
*/
static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
if (sys_fl->fl_type == F_WRLCK)
return 1;
if (caller_fl->fl_type == F_WRLCK)
return 1;
return 0;
}
/* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
* checking before calling the locks_conflict().
*/
static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
/* POSIX locks owned by the same process do not conflict with
* each other.
*/
if (!IS_POSIX(sys_fl) || posix_same_owner(caller_fl, sys_fl))
return (0);
/* Check whether they overlap */
if (!locks_overlap(caller_fl, sys_fl))
return 0;
return (locks_conflict(caller_fl, sys_fl));
}
/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
* checking before calling the locks_conflict().
*/
static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
/* FLOCK locks referring to the same filp do not conflict with
* each other.
*/
if (!IS_FLOCK(sys_fl) || (caller_fl->fl_file == sys_fl->fl_file))
return (0);
if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
return 0;
return (locks_conflict(caller_fl, sys_fl));
}
static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout)
{
int result = 0;
DECLARE_WAITQUEUE(wait, current);
__set_current_state(TASK_INTERRUPTIBLE);
add_wait_queue(fl_wait, &wait);
if (timeout == 0)
schedule();
else
result = schedule_timeout(timeout);
if (signal_pending(current))
result = -ERESTARTSYS;
remove_wait_queue(fl_wait, &wait);
__set_current_state(TASK_RUNNING);
return result;
}
static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time)
{
int result;
locks_insert_block(blocker, waiter);
result = interruptible_sleep_on_locked(&waiter->fl_wait, time);
__locks_delete_block(waiter);
return result;
}
struct file_lock *
posix_test_lock(struct file *filp, struct file_lock *fl)
{
struct file_lock *cfl;
lock_kernel();
for (cfl = filp->f_dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
if (!IS_POSIX(cfl))
continue;
if (posix_locks_conflict(cfl, fl))
break;
}
unlock_kernel();
return (cfl);
}
EXPORT_SYMBOL(posix_test_lock);
/* This function tests for deadlock condition before putting a process to
* sleep. The detection scheme is no longer recursive. Recursive was neat,
* but dangerous - we risked stack corruption if the lock data was bad, or
* if the recursion was too deep for any other reason.
*
* We rely on the fact that a task can only be on one lock's wait queue
* at a time. When we find blocked_task on a wait queue we can re-search
* with blocked_task equal to that queue's owner, until either blocked_task
* isn't found, or blocked_task is found on a queue owned by my_task.
*
* Note: the above assumption may not be true when handling lock requests
* from a broken NFS client. But broken NFS clients have a lot more to
* worry about than proper deadlock detection anyway... --okir
*/
int posix_locks_deadlock(struct file_lock *caller_fl,
struct file_lock *block_fl)
{
struct list_head *tmp;
next_task:
if (posix_same_owner(caller_fl, block_fl))
return 1;
list_for_each(tmp, &blocked_list) {
struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
if (posix_same_owner(fl, block_fl)) {
fl = fl->fl_next;
block_fl = fl;
goto next_task;
}
}
return 0;
}
EXPORT_SYMBOL(posix_locks_deadlock);
/* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
* at the head of the list, but that's secret knowledge known only to
* flock_lock_file and posix_lock_file.
*/
static int flock_lock_file(struct file *filp, struct file_lock *new_fl)
{
struct file_lock **before;
struct inode * inode = filp->f_dentry->d_inode;
int error = 0;
int found = 0;
lock_kernel();
for_each_lock(inode, before) {
struct file_lock *fl = *before;
if (IS_POSIX(fl))
break;
if (IS_LEASE(fl))
continue;
if (filp != fl->fl_file)
continue;
if (new_fl->fl_type == fl->fl_type)
goto out;
found = 1;
locks_delete_lock(before);
break;
}
unlock_kernel();
if (new_fl->fl_type == F_UNLCK)
return 0;
/*
* If a higher-priority process was blocked on the old file lock,
* give it the opportunity to lock the file.
*/
if (found)
cond_resched();
lock_kernel();
for_each_lock(inode, before) {
struct file_lock *fl = *before;
if (IS_POSIX(fl))
break;
if (IS_LEASE(fl))
continue;
if (!flock_locks_conflict(new_fl, fl))
continue;
error = -EAGAIN;
if (new_fl->fl_flags & FL_SLEEP) {
locks_insert_block(fl, new_fl);
}
goto out;
}
locks_insert_lock(&inode->i_flock, new_fl);
error = 0;
out:
unlock_kernel();
return error;
}
EXPORT_SYMBOL(posix_lock_file);
static int __posix_lock_file(struct inode *inode, struct file_lock *request)
{
struct file_lock *fl;
struct file_lock *new_fl, *new_fl2;
struct file_lock *left = NULL;
struct file_lock *right = NULL;
struct file_lock **before;
int error, added = 0;
/*
* We may need two file_lock structures for this operation,
* so we get them in advance to avoid races.
*/
new_fl = locks_alloc_lock();
new_fl2 = locks_alloc_lock();
lock_kernel();
if (request->fl_type != F_UNLCK) {
for_each_lock(inode, before) {
struct file_lock *fl = *before;
if (!IS_POSIX(fl))
continue;
if (!posix_locks_conflict(request, fl))
continue;
error = -EAGAIN;
if (!(request->fl_flags & FL_SLEEP))
goto out;
error = -EDEADLK;
if (posix_locks_deadlock(request, fl))
goto out;
error = -EAGAIN;
locks_insert_block(fl, request);
goto out;
}
}
/* If we're just looking for a conflict, we're done. */
error = 0;
if (request->fl_flags & FL_ACCESS)
goto out;
error = -ENOLCK; /* "no luck" */
if (!(new_fl && new_fl2))
goto out;
/*
* We've allocated the new locks in advance, so there are no
* errors possible (and no blocking operations) from here on.
*
* Find the first old lock with the same owner as the new lock.
*/
before = &inode->i_flock;
/* First skip locks owned by other processes. */
while ((fl = *before) && (!IS_POSIX(fl) ||
!posix_same_owner(request, fl))) {
before = &fl->fl_next;
}
/* Process locks with this owner. */
while ((fl = *before) && posix_same_owner(request, fl)) {
/* Detect adjacent or overlapping regions (if same lock type)
*/
if (request->fl_type == fl->fl_type) {
if (fl->fl_end < request->fl_start - 1)
goto next_lock;
/* If the next lock in the list has entirely bigger
* addresses than the new one, insert the lock here.
*/
if (fl->fl_start > request->fl_end + 1)
break;
/* If we come here, the new and old lock are of the
* same type and adjacent or overlapping. Make one
* lock yielding from the lower start address of both
* locks to the higher end address.
*/
if (fl->fl_start > request->fl_start)
fl->fl_start = request->fl_start;
else
request->fl_start = fl->fl_start;
if (fl->fl_end < request->fl_end)
fl->fl_end = request->fl_end;
else
request->fl_end = fl->fl_end;
if (added) {
locks_delete_lock(before);
continue;
}
request = fl;
added = 1;
}
else {
/* Processing for different lock types is a bit
* more complex.
*/
if (fl->fl_end < request->fl_start)
goto next_lock;
if (fl->fl_start > request->fl_end)
break;
if (request->fl_type == F_UNLCK)
added = 1;
if (fl->fl_start < request->fl_start)
left = fl;
/* If the next lock in the list has a higher end
* address than the new one, insert the new one here.
*/
if (fl->fl_end > request->fl_end) {
right = fl;
break;
}
if (fl->fl_start >= request->fl_start) {
/* The new lock completely replaces an old
* one (This may happen several times).
*/
if (added) {
locks_delete_lock(before);
continue;
}
/* Replace the old lock with the new one.
* Wake up anybody waiting for the old one,
* as the change in lock type might satisfy
* their needs.
*/
locks_wake_up_blocks(fl);
fl->fl_start = request->fl_start;
fl->fl_end = request->fl_end;
fl->fl_type = request->fl_type;
fl->fl_u = request->fl_u;
request = fl;
added = 1;
}
}
/* Go on to next lock.
*/
next_lock:
before = &fl->fl_next;
}
error = 0;
if (!added) {
if (request->fl_type == F_UNLCK)
goto out;
locks_copy_lock(new_fl, request);
locks_insert_lock(before, new_fl);
new_fl = NULL;
}
if (right) {
if (left == right) {
/* The new lock breaks the old one in two pieces,
* so we have to use the second new lock.
*/
left = new_fl2;
new_fl2 = NULL;
locks_copy_lock(left, right);
locks_insert_lock(before, left);
}
right->fl_start = request->fl_end + 1;
locks_wake_up_blocks(right);
}
if (left) {
left->fl_end = request->fl_start - 1;
locks_wake_up_blocks(left);
}
out:
unlock_kernel();
/*
* Free any unused locks.
*/
if (new_fl)
locks_free_lock(new_fl);
if (new_fl2)
locks_free_lock(new_fl2);
return error;
}
/**
* posix_lock_file - Apply a POSIX-style lock to a file
* @filp: The file to apply the lock to
* @fl: The lock to be applied
*
* Add a POSIX style lock to a file.
* We merge adjacent & overlapping locks whenever possible.
* POSIX locks are sorted by owner task, then by starting address
*/
int posix_lock_file(struct file *filp, struct file_lock *fl)
{
return __posix_lock_file(filp->f_dentry->d_inode, fl);
}
/**
* posix_lock_file_wait - Apply a POSIX-style lock to a file
* @filp: The file to apply the lock to
* @fl: The lock to be applied
*
* Add a POSIX style lock to a file.
* We merge adjacent & overlapping locks whenever possible.
* POSIX locks are sorted by owner task, then by starting address
*/
int posix_lock_file_wait(struct file *filp, struct file_lock *fl)
{
int error;
might_sleep ();
for (;;) {
error = __posix_lock_file(filp->f_dentry->d_inode, fl);
if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
break;
error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
if (!error)
continue;
locks_delete_block(fl);
break;
}
return error;
}
EXPORT_SYMBOL(posix_lock_file_wait);
/**
* locks_mandatory_locked - Check for an active lock
* @inode: the file to check
*
* Searches the inode's list of locks to find any POSIX locks which conflict.
* This function is called from locks_verify_locked() only.
*/
int locks_mandatory_locked(struct inode *inode)
{
fl_owner_t owner = current->files;
struct file_lock *fl;
/*
* Search the lock list for this inode for any POSIX locks.
*/
lock_kernel();
for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
if (!IS_POSIX(fl))
continue;
if (fl->fl_owner != owner)
break;
}
unlock_kernel();
return fl ? -EAGAIN : 0;
}
/**
* locks_mandatory_area - Check for a conflicting lock
* @read_write: %FLOCK_VERIFY_WRITE for exclusive access, %FLOCK_VERIFY_READ
* for shared
* @inode: the file to check
* @filp: how the file was opened (if it was)
* @offset: start of area to check
* @count: length of area to check
*
* Searches the inode's list of locks to find any POSIX locks which conflict.
* This function is called from rw_verify_area() and
* locks_verify_truncate().
*/
int locks_mandatory_area(int read_write, struct inode *inode,
struct file *filp, loff_t offset,
size_t count)
{
struct file_lock fl;
int error;
locks_init_lock(&fl);
fl.fl_owner = current->files;
fl.fl_pid = current->tgid;
fl.fl_file = filp;
fl.fl_flags = FL_POSIX | FL_ACCESS;
if (filp && !(filp->f_flags & O_NONBLOCK))
fl.fl_flags |= FL_SLEEP;
fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
fl.fl_start = offset;
fl.fl_end = offset + count - 1;
for (;;) {
error = __posix_lock_file(inode, &fl);
if (error != -EAGAIN)
break;
if (!(fl.fl_flags & FL_SLEEP))
break;
error = wait_event_interruptible(fl.fl_wait, !fl.fl_next);
if (!error) {
/*
* If we've been sleeping someone might have
* changed the permissions behind our back.
*/
if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
continue;
}
locks_delete_block(&fl);
break;
}
return error;
}
EXPORT_SYMBOL(locks_mandatory_area);
/* We already had a lease on this file; just change its type */
int lease_modify(struct file_lock **before, int arg)
{
struct file_lock *fl = *before;
int error = assign_type(fl, arg);
if (error)
return error;
locks_wake_up_blocks(fl);
if (arg == F_UNLCK)
locks_delete_lock(before);
return 0;
}
EXPORT_SYMBOL(lease_modify);
static void time_out_leases(struct inode *inode)
{
struct file_lock **before;
struct file_lock *fl;
before = &inode->i_flock;
while ((fl = *before) && IS_LEASE(fl) && (fl->fl_type & F_INPROGRESS)) {
if ((fl->fl_break_time == 0)
|| time_before(jiffies, fl->fl_break_time)) {
before = &fl->fl_next;
continue;
}
printk(KERN_INFO "lease broken - owner pid = %d\n", fl->fl_pid);
lease_modify(before, fl->fl_type & ~F_INPROGRESS);
if (fl == *before) /* lease_modify may have freed fl */
before = &fl->fl_next;
}
}
/**
* __break_lease - revoke all outstanding leases on file
* @inode: the inode of the file to return
* @mode: the open mode (read or write)
*
* break_lease (inlined for speed) has checked there already
* is a lease on this file. Leases are broken on a call to open()
* or truncate(). This function can sleep unless you
* specified %O_NONBLOCK to your open().
*/
int __break_lease(struct inode *inode, unsigned int mode)
{
int error = 0, future;
struct file_lock *new_fl, *flock;
struct file_lock *fl;
int alloc_err;
unsigned long break_time;
int i_have_this_lease = 0;
alloc_err = lease_alloc(NULL, mode & FMODE_WRITE ? F_WRLCK : F_RDLCK,
&new_fl);
lock_kernel();
time_out_leases(inode);
flock = inode->i_flock;
if ((flock == NULL) || !IS_LEASE(flock))
goto out;
for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
if (fl->fl_owner == current->files)
i_have_this_lease = 1;
if (mode & FMODE_WRITE) {
/* If we want write access, we have to revoke any lease. */
future = F_UNLCK | F_INPROGRESS;
} else if (flock->fl_type & F_INPROGRESS) {
/* If the lease is already being broken, we just leave it */
future = flock->fl_type;
} else if (flock->fl_type & F_WRLCK) {
/* Downgrade the exclusive lease to a read-only lease. */
future = F_RDLCK | F_INPROGRESS;
} else {
/* the existing lease was read-only, so we can read too. */
goto out;
}
if (alloc_err && !i_have_this_lease && ((mode & O_NONBLOCK) == 0)) {
error = alloc_err;
goto out;
}
break_time = 0;
if (lease_break_time > 0) {
break_time = jiffies + lease_break_time * HZ;
if (break_time == 0)
break_time++; /* so that 0 means no break time */
}
for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next) {
if (fl->fl_type != future) {
fl->fl_type = future;
fl->fl_break_time = break_time;
/* lease must have lmops break callback */
fl->fl_lmops->fl_break(fl);
}
}
if (i_have_this_lease || (mode & O_NONBLOCK)) {
error = -EWOULDBLOCK;
goto out;
}
restart:
break_time = flock->fl_break_time;
if (break_time != 0) {
break_time -= jiffies;
if (break_time == 0)
break_time++;
}
error = locks_block_on_timeout(flock, new_fl, break_time);
if (error >= 0) {
if (error == 0)
time_out_leases(inode);
/* Wait for the next lease that has not been broken yet */
for (flock = inode->i_flock; flock && IS_LEASE(flock);
flock = flock->fl_next) {
if (flock->fl_type & F_INPROGRESS)
goto restart;
}
error = 0;
}
out:
unlock_kernel();
if (!alloc_err)
locks_free_lock(new_fl);
return error;
}
EXPORT_SYMBOL(__break_lease);
/**
* lease_get_mtime
* @inode: the inode
* @time: pointer to a timespec which will contain the last modified time
*
* This is to force NFS clients to flush their caches for files with
* exclusive leases. The justification is that if someone has an
* exclusive lease, then they could be modifiying it.
*/
void lease_get_mtime(struct inode *inode, struct timespec *time)
{
struct file_lock *flock = inode->i_flock;
if (flock && IS_LEASE(flock) && (flock->fl_type & F_WRLCK))
*time = current_fs_time(inode->i_sb);
else
*time = inode->i_mtime;
}
EXPORT_SYMBOL(lease_get_mtime);
/**
* fcntl_getlease - Enquire what lease is currently active
* @filp: the file
*
* The value returned by this function will be one of
* (if no lease break is pending):
*
* %F_RDLCK to indicate a shared lease is held.
*
* %F_WRLCK to indicate an exclusive lease is held.
*
* %F_UNLCK to indicate no lease is held.
*
* (if a lease break is pending):
*
* %F_RDLCK to indicate an exclusive lease needs to be
* changed to a shared lease (or removed).
*
* %F_UNLCK to indicate the lease needs to be removed.
*
* XXX: sfr & willy disagree over whether F_INPROGRESS
* should be returned to userspace.
*/
int fcntl_getlease(struct file *filp)
{
struct file_lock *fl;
int type = F_UNLCK;
lock_kernel();
time_out_leases(filp->f_dentry->d_inode);
for (fl = filp->f_dentry->d_inode->i_flock; fl && IS_LEASE(fl);
fl = fl->fl_next) {
if (fl->fl_file == filp) {
type = fl->fl_type & ~F_INPROGRESS;
break;
}
}
unlock_kernel();
return type;
}
/**
* __setlease - sets a lease on an open file
* @filp: file pointer
* @arg: type of lease to obtain
* @flp: input - file_lock to use, output - file_lock inserted
*
* The (input) flp->fl_lmops->fl_break function is required
* by break_lease().
*
* Called with kernel lock held.
*/
static int __setlease(struct file *filp, long arg, struct file_lock **flp)
{
struct file_lock *fl, **before, **my_before = NULL, *lease;
struct dentry *dentry = filp->f_dentry;
struct inode *inode = dentry->d_inode;
int error, rdlease_count = 0, wrlease_count = 0;
time_out_leases(inode);
error = -EINVAL;
if (!flp || !(*flp) || !(*flp)->fl_lmops || !(*flp)->fl_lmops->fl_break)
goto out;
lease = *flp;
error = -EAGAIN;
if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
goto out;
if ((arg == F_WRLCK)
&& ((atomic_read(&dentry->d_count) > 1)
|| (atomic_read(&inode->i_count) > 1)))
goto out;
/*
* At this point, we know that if there is an exclusive
* lease on this file, then we hold it on this filp
* (otherwise our open of this file would have blocked).
* And if we are trying to acquire an exclusive lease,
* then the file is not open by anyone (including us)
* except for this filp.
*/
for (before = &inode->i_flock;
((fl = *before) != NULL) && IS_LEASE(fl);
before = &fl->fl_next) {
if (lease->fl_lmops->fl_mylease(fl, lease))
my_before = before;
else if (fl->fl_type == (F_INPROGRESS | F_UNLCK))
/*
* Someone is in the process of opening this
* file for writing so we may not take an
* exclusive lease on it.
*/
wrlease_count++;
else
rdlease_count++;
}
if ((arg == F_RDLCK && (wrlease_count > 0)) ||
(arg == F_WRLCK && ((rdlease_count + wrlease_count) > 0)))
goto out;
if (my_before != NULL) {
error = lease->fl_lmops->fl_change(my_before, arg);
goto out;
}
error = 0;
if (arg == F_UNLCK)
goto out;
error = -EINVAL;
if (!leases_enable)
goto out;
error = lease_alloc(filp, arg, &fl);
if (error)
goto out;
locks_copy_lock(fl, lease);
locks_insert_lock(before, fl);
*flp = fl;
out:
return error;
}
/**
* setlease - sets a lease on an open file
* @filp: file pointer
* @arg: type of lease to obtain
* @lease: file_lock to use
*
* Call this to establish a lease on the file.
* The fl_lmops fl_break function is required by break_lease
*/
int setlease(struct file *filp, long arg, struct file_lock **lease)
{
struct dentry *dentry = filp->f_dentry;
struct inode *inode = dentry->d_inode;
int error;
if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
return -EACCES;
if (!S_ISREG(inode->i_mode))
return -EINVAL;
error = security_file_lock(filp, arg);
if (error)
return error;
lock_kernel();
error = __setlease(filp, arg, lease);
unlock_kernel();
return error;
}
EXPORT_SYMBOL(setlease);
/**
* fcntl_setlease - sets a lease on an open file
* @fd: open file descriptor
* @filp: file pointer
* @arg: type of lease to obtain
*
* Call this fcntl to establish a lease on the file.
* Note that you also need to call %F_SETSIG to
* receive a signal when the lease is broken.
*/
int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
{
struct file_lock fl, *flp = &fl;
struct dentry *dentry = filp->f_dentry;
struct inode *inode = dentry->d_inode;
int error;
if ((current->fsuid != inode->i_uid) && !capable(CAP_LEASE))
return -EACCES;
if (!S_ISREG(inode->i_mode))
return -EINVAL;
error = security_file_lock(filp, arg);
if (error)
return error;
locks_init_lock(&fl);
error = lease_init(filp, arg, &fl);
if (error)
return error;
lock_kernel();
error = __setlease(filp, arg, &flp);
if (error)
goto out_unlock;
error = fasync_helper(fd, filp, 1, &flp->fl_fasync);
if (error < 0) {
/* remove lease just inserted by __setlease */
flp->fl_type = F_UNLCK | F_INPROGRESS;
flp->fl_break_time = jiffies- 10;
time_out_leases(inode);
goto out_unlock;
}
error = f_setown(filp, current->pid, 0);
out_unlock:
unlock_kernel();
return error;
}
/**
* flock_lock_file_wait - Apply a FLOCK-style lock to a file
* @filp: The file to apply the lock to
* @fl: The lock to be applied
*
* Add a FLOCK style lock to a file.
*/
int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
{
int error;
might_sleep();
for (;;) {
error = flock_lock_file(filp, fl);
if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
break;
error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
if (!error)
continue;
locks_delete_block(fl);
break;
}
return error;
}
EXPORT_SYMBOL(flock_lock_file_wait);
/**
* sys_flock: - flock() system call.
* @fd: the file descriptor to lock.
* @cmd: the type of lock to apply.
*
* Apply a %FL_FLOCK style lock to an open file descriptor.
* The @cmd can be one of
*
* %LOCK_SH -- a shared lock.
*
* %LOCK_EX -- an exclusive lock.
*
* %LOCK_UN -- remove an existing lock.
*
* %LOCK_MAND -- a `mandatory' flock. This exists to emulate Windows Share Modes.
*
* %LOCK_MAND can be combined with %LOCK_READ or %LOCK_WRITE to allow other
* processes read and write access respectively.
*/
asmlinkage long sys_flock(unsigned int fd, unsigned int cmd)
{
struct file *filp;
struct file_lock *lock;
int can_sleep, unlock;
int error;
error = -EBADF;
filp = fget(fd);
if (!filp)
goto out;
can_sleep = !(cmd & LOCK_NB);
cmd &= ~LOCK_NB;
unlock = (cmd == LOCK_UN);
if (!unlock && !(cmd & LOCK_MAND) && !(filp->f_mode & 3))
goto out_putf;
error = flock_make_lock(filp, &lock, cmd);
if (error)
goto out_putf;
if (can_sleep)
lock->fl_flags |= FL_SLEEP;
error = security_file_lock(filp, cmd);
if (error)
goto out_free;
if (filp->f_op && filp->f_op->flock)
error = filp->f_op->flock(filp,
(can_sleep) ? F_SETLKW : F_SETLK,
lock);
else
error = flock_lock_file_wait(filp, lock);
out_free:
if (list_empty(&lock->fl_link)) {
locks_free_lock(lock);
}
out_putf:
fput(filp);
out:
return error;
}
/* Report the first existing lock that would conflict with l.
* This implements the F_GETLK command of fcntl().
*/
int fcntl_getlk(struct file *filp, struct flock __user *l)
{
struct file_lock *fl, file_lock;
struct flock flock;
int error;
error = -EFAULT;
if (copy_from_user(&flock, l, sizeof(flock)))
goto out;
error = -EINVAL;
if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
goto out;
error = flock_to_posix_lock(filp, &file_lock, &flock);
if (error)
goto out;
if (filp->f_op && filp->f_op->lock) {
error = filp->f_op->lock(filp, F_GETLK, &file_lock);
if (file_lock.fl_ops && file_lock.fl_ops->fl_release_private)
file_lock.fl_ops->fl_release_private(&file_lock);
if (error < 0)
goto out;
else
fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
} else {
fl = posix_test_lock(filp, &file_lock);
}
flock.l_type = F_UNLCK;
if (fl != NULL) {
flock.l_pid = fl->fl_pid;
#if BITS_PER_LONG == 32
/*
* Make sure we can represent the posix lock via
* legacy 32bit flock.
*/
error = -EOVERFLOW;
if (fl->fl_start > OFFT_OFFSET_MAX)
goto out;
if ((fl->fl_end != OFFSET_MAX)
&& (fl->fl_end > OFFT_OFFSET_MAX))
goto out;
#endif
flock.l_start = fl->fl_start;
flock.l_len = fl->fl_end == OFFSET_MAX ? 0 :
fl->fl_end - fl->fl_start + 1;
flock.l_whence = 0;
flock.l_type = fl->fl_type;
}
error = -EFAULT;
if (!copy_to_user(l, &flock, sizeof(flock)))
error = 0;
out:
return error;
}
/* Apply the lock described by l to an open file descriptor.
* This implements both the F_SETLK and F_SETLKW commands of fcntl().
*/
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
struct flock __user *l)
{
struct file_lock *file_lock = locks_alloc_lock();
struct flock flock;
struct inode *inode;
int error;
if (file_lock == NULL)
return -ENOLCK;
/*
* This might block, so we do it before checking the inode.
*/
error = -EFAULT;
if (copy_from_user(&flock, l, sizeof(flock)))
goto out;
inode = filp->f_dentry->d_inode;
/* Don't allow mandatory locks on files that may be memory mapped
* and shared.
*/
if (IS_MANDLOCK(inode) &&
(inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
mapping_writably_mapped(filp->f_mapping)) {
error = -EAGAIN;
goto out;
}
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
again:
error = flock_to_posix_lock(filp, file_lock, &flock);
if (error)
goto out;
if (cmd == F_SETLKW) {
file_lock->fl_flags |= FL_SLEEP;
}
error = -EBADF;
switch (flock.l_type) {
case F_RDLCK:
if (!(filp->f_mode & FMODE_READ))
goto out;
break;
case F_WRLCK:
if (!(filp->f_mode & FMODE_WRITE))
goto out;
break;
case F_UNLCK:
break;
default:
error = -EINVAL;
goto out;
}
error = security_file_lock(filp, file_lock->fl_type);
if (error)
goto out;
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
if (filp->f_op && filp->f_op->lock != NULL)
error = filp->f_op->lock(filp, cmd, file_lock);
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
else {
for (;;) {
error = __posix_lock_file(inode, file_lock);
if ((error != -EAGAIN) || (cmd == F_SETLK))
break;
error = wait_event_interruptible(file_lock->fl_wait,
!file_lock->fl_next);
if (!error)
continue;
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
locks_delete_block(file_lock);
break;
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
}
}
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
/*
* Attempt to detect a close/fcntl race and recover by
* releasing the lock that was just acquired.
*/
if (!error && fcheck(fd) != filp && flock.l_type != F_UNLCK) {
flock.l_type = F_UNLCK;
goto again;
}
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
out:
locks_free_lock(file_lock);
return error;
}
#if BITS_PER_LONG == 32
/* Report the first existing lock that would conflict with l.
* This implements the F_GETLK command of fcntl().
*/
int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
{
struct file_lock *fl, file_lock;
struct flock64 flock;
int error;
error = -EFAULT;
if (copy_from_user(&flock, l, sizeof(flock)))
goto out;
error = -EINVAL;
if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
goto out;
error = flock64_to_posix_lock(filp, &file_lock, &flock);
if (error)
goto out;
if (filp->f_op && filp->f_op->lock) {
error = filp->f_op->lock(filp, F_GETLK, &file_lock);
if (file_lock.fl_ops && file_lock.fl_ops->fl_release_private)
file_lock.fl_ops->fl_release_private(&file_lock);
if (error < 0)
goto out;
else
fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
} else {
fl = posix_test_lock(filp, &file_lock);
}
flock.l_type = F_UNLCK;
if (fl != NULL) {
flock.l_pid = fl->fl_pid;
flock.l_start = fl->fl_start;
flock.l_len = fl->fl_end == OFFSET_MAX ? 0 :
fl->fl_end - fl->fl_start + 1;
flock.l_whence = 0;
flock.l_type = fl->fl_type;
}
error = -EFAULT;
if (!copy_to_user(l, &flock, sizeof(flock)))
error = 0;
out:
return error;
}
/* Apply the lock described by l to an open file descriptor.
* This implements both the F_SETLK and F_SETLKW commands of fcntl().
*/
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
struct flock64 __user *l)
{
struct file_lock *file_lock = locks_alloc_lock();
struct flock64 flock;
struct inode *inode;
int error;
if (file_lock == NULL)
return -ENOLCK;
/*
* This might block, so we do it before checking the inode.
*/
error = -EFAULT;
if (copy_from_user(&flock, l, sizeof(flock)))
goto out;
inode = filp->f_dentry->d_inode;
/* Don't allow mandatory locks on files that may be memory mapped
* and shared.
*/
if (IS_MANDLOCK(inode) &&
(inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
mapping_writably_mapped(filp->f_mapping)) {
error = -EAGAIN;
goto out;
}
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
again:
error = flock64_to_posix_lock(filp, file_lock, &flock);
if (error)
goto out;
if (cmd == F_SETLKW64) {
file_lock->fl_flags |= FL_SLEEP;
}
error = -EBADF;
switch (flock.l_type) {
case F_RDLCK:
if (!(filp->f_mode & FMODE_READ))
goto out;
break;
case F_WRLCK:
if (!(filp->f_mode & FMODE_WRITE))
goto out;
break;
case F_UNLCK:
break;
default:
error = -EINVAL;
goto out;
}
error = security_file_lock(filp, file_lock->fl_type);
if (error)
goto out;
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
if (filp->f_op && filp->f_op->lock != NULL)
error = filp->f_op->lock(filp, cmd, file_lock);
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
else {
for (;;) {
error = __posix_lock_file(inode, file_lock);
if ((error != -EAGAIN) || (cmd == F_SETLK64))
break;
error = wait_event_interruptible(file_lock->fl_wait,
!file_lock->fl_next);
if (!error)
continue;
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
locks_delete_block(file_lock);
break;
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
}
}
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
/*
* Attempt to detect a close/fcntl race and recover by
* releasing the lock that was just acquired.
*/
if (!error && fcheck(fd) != filp && flock.l_type != F_UNLCK) {
flock.l_type = F_UNLCK;
goto again;
}
out:
locks_free_lock(file_lock);
return error;
}
#endif /* BITS_PER_LONG == 32 */
/*
* This function is called when the file is being removed
* from the task's fd array. POSIX locks belonging to this task
* are deleted at this time.
*/
void locks_remove_posix(struct file *filp, fl_owner_t owner)
{
struct file_lock lock, **before;
/*
* If there are no locks held on this file, we don't need to call
* posix_lock_file(). Another process could be setting a lock on this
* file at the same time, but we wouldn't remove that lock anyway.
*/
before = &filp->f_dentry->d_inode->i_flock;
if (*before == NULL)
return;
lock.fl_type = F_UNLCK;
lock.fl_flags = FL_POSIX;
lock.fl_start = 0;
lock.fl_end = OFFSET_MAX;
lock.fl_owner = owner;
lock.fl_pid = current->tgid;
lock.fl_file = filp;
lock.fl_ops = NULL;
lock.fl_lmops = NULL;
if (filp->f_op && filp->f_op->lock != NULL) {
filp->f_op->lock(filp, F_SETLK, &lock);
goto out;
}
/* Can't use posix_lock_file here; we need to remove it no matter
* which pid we have.
*/
lock_kernel();
while (*before != NULL) {
struct file_lock *fl = *before;
if (IS_POSIX(fl) && posix_same_owner(fl, &lock)) {
locks_delete_lock(before);
continue;
}
before = &fl->fl_next;
}
unlock_kernel();
out:
if (lock.fl_ops && lock.fl_ops->fl_release_private)
lock.fl_ops->fl_release_private(&lock);
}
EXPORT_SYMBOL(locks_remove_posix);
/*
* This function is called on the last close of an open file.
*/
void locks_remove_flock(struct file *filp)
{
struct inode * inode = filp->f_dentry->d_inode;
struct file_lock *fl;
struct file_lock **before;
if (!inode->i_flock)
return;
if (filp->f_op && filp->f_op->flock) {
struct file_lock fl = {
.fl_pid = current->tgid,
.fl_file = filp,
.fl_flags = FL_FLOCK,
.fl_type = F_UNLCK,
.fl_end = OFFSET_MAX,
};
filp->f_op->flock(filp, F_SETLKW, &fl);
if (fl.fl_ops && fl.fl_ops->fl_release_private)
fl.fl_ops->fl_release_private(&fl);
}
lock_kernel();
before = &inode->i_flock;
while ((fl = *before) != NULL) {
if (fl->fl_file == filp) {
[PATCH] stale POSIX lock handling I believe that there is a problem with the handling of POSIX locks, which the attached patch should address. The problem appears to be a race between fcntl(2) and close(2). A multithreaded application could close a file descriptor at the same time as it is trying to acquire a lock using the same file descriptor. I would suggest that that multithreaded application is not providing the proper synchronization for itself, but the OS should still behave correctly. SUS3 (Single UNIX Specification Version 3, read: POSIX) indicates that when a file descriptor is closed, that all POSIX locks on the file, owned by the process which closed the file descriptor, should be released. The trick here is when those locks are released. The current code releases all locks which exist when close is processing, but any locks in progress are handled when the last reference to the open file is released. There are three cases to consider. One is the simple case, a multithreaded (mt) process has a file open and races to close it and acquire a lock on it. In this case, the close will release one reference to the open file and when the fcntl is done, it will release the other reference. For this situation, no locks should exist on the file when both the close and fcntl operations are done. The current system will handle this case because the last reference to the open file is being released. The second case is when the mt process has dup(2)'d the file descriptor. The close will release one reference to the file and the fcntl, when done, will release another, but there will still be at least one more reference to the open file. One could argue that the existence of a lock on the file after the close has completed is okay, because it was acquired after the close operation and there is still a way for the application to release the lock on the file, using an existing file descriptor. The third case is when the mt process has forked, after opening the file and either before or after becoming an mt process. In this case, each process would hold a reference to the open file. For each process, this degenerates to first case above. However, the lock continues to exist until both processes have released their references to the open file. This lock could block other lock requests. The changes to release the lock when the last reference to the open file aren't quite right because they would allow the lock to exist as long as there was a reference to the open file. This is too long. The new proposed solution is to add support in the fcntl code path to detect a race with close and then to release the lock which was just acquired when such as race is detected. This causes locks to be released in a timely fashion and for the system to conform to the POSIX semantic specification. This was tested by instrumenting a kernel to detect the handling locks and then running a program which generates case #3 above. A dangling lock could be reliably generated. When the changes to detect the close/fcntl race were added, a dangling lock could no longer be generated. Cc: Matthew Wilcox <willy@debian.org> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-07-27 18:45:09 +00:00
if (IS_FLOCK(fl)) {
locks_delete_lock(before);
continue;
}
if (IS_LEASE(fl)) {
lease_modify(before, F_UNLCK);
continue;
}
/* What? */
BUG();
}
before = &fl->fl_next;
}
unlock_kernel();
}
/**
* posix_block_lock - blocks waiting for a file lock
* @blocker: the lock which is blocking
* @waiter: the lock which conflicts and has to wait
*
* lockd needs to block waiting for locks.
*/
void
posix_block_lock(struct file_lock *blocker, struct file_lock *waiter)
{
locks_insert_block(blocker, waiter);
}
EXPORT_SYMBOL(posix_block_lock);
/**
* posix_unblock_lock - stop waiting for a file lock
* @filp: how the file was opened
* @waiter: the lock which was waiting
*
* lockd needs to block waiting for locks.
*/
void
posix_unblock_lock(struct file *filp, struct file_lock *waiter)
{
/*
* A remote machine may cancel the lock request after it's been
* granted locally. If that happens, we need to delete the lock.
*/
lock_kernel();
if (waiter->fl_next) {
__locks_delete_block(waiter);
unlock_kernel();
} else {
unlock_kernel();
waiter->fl_type = F_UNLCK;
posix_lock_file(filp, waiter);
}
}
EXPORT_SYMBOL(posix_unblock_lock);
static void lock_get_status(char* out, struct file_lock *fl, int id, char *pfx)
{
struct inode *inode = NULL;
if (fl->fl_file != NULL)
inode = fl->fl_file->f_dentry->d_inode;
out += sprintf(out, "%d:%s ", id, pfx);
if (IS_POSIX(fl)) {
out += sprintf(out, "%6s %s ",
(fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
(inode == NULL) ? "*NOINODE*" :
(IS_MANDLOCK(inode) &&
(inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
"MANDATORY" : "ADVISORY ");
} else if (IS_FLOCK(fl)) {
if (fl->fl_type & LOCK_MAND) {
out += sprintf(out, "FLOCK MSNFS ");
} else {
out += sprintf(out, "FLOCK ADVISORY ");
}
} else if (IS_LEASE(fl)) {
out += sprintf(out, "LEASE ");
if (fl->fl_type & F_INPROGRESS)
out += sprintf(out, "BREAKING ");
else if (fl->fl_file)
out += sprintf(out, "ACTIVE ");
else
out += sprintf(out, "BREAKER ");
} else {
out += sprintf(out, "UNKNOWN UNKNOWN ");
}
if (fl->fl_type & LOCK_MAND) {
out += sprintf(out, "%s ",
(fl->fl_type & LOCK_READ)
? (fl->fl_type & LOCK_WRITE) ? "RW " : "READ "
: (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
} else {
out += sprintf(out, "%s ",
(fl->fl_type & F_INPROGRESS)
? (fl->fl_type & F_UNLCK) ? "UNLCK" : "READ "
: (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
}
if (inode) {
#ifdef WE_CAN_BREAK_LSLK_NOW
out += sprintf(out, "%d %s:%ld ", fl->fl_pid,
inode->i_sb->s_id, inode->i_ino);
#else
/* userspace relies on this representation of dev_t ;-( */
out += sprintf(out, "%d %02x:%02x:%ld ", fl->fl_pid,
MAJOR(inode->i_sb->s_dev),
MINOR(inode->i_sb->s_dev), inode->i_ino);
#endif
} else {
out += sprintf(out, "%d <none>:0 ", fl->fl_pid);
}
if (IS_POSIX(fl)) {
if (fl->fl_end == OFFSET_MAX)
out += sprintf(out, "%Ld EOF\n", fl->fl_start);
else
out += sprintf(out, "%Ld %Ld\n", fl->fl_start,
fl->fl_end);
} else {
out += sprintf(out, "0 EOF\n");
}
}
static void move_lock_status(char **p, off_t* pos, off_t offset)
{
int len;
len = strlen(*p);
if(*pos >= offset) {
/* the complete line is valid */
*p += len;
*pos += len;
return;
}
if(*pos+len > offset) {
/* use the second part of the line */
int i = offset-*pos;
memmove(*p,*p+i,len-i);
*p += len-i;
*pos += len;
return;
}
/* discard the complete line */
*pos += len;
}
/**
* get_locks_status - reports lock usage in /proc/locks
* @buffer: address in userspace to write into
* @start: ?
* @offset: how far we are through the buffer
* @length: how much to read
*/
int get_locks_status(char *buffer, char **start, off_t offset, int length)
{
struct list_head *tmp;
char *q = buffer;
off_t pos = 0;
int i = 0;
lock_kernel();
list_for_each(tmp, &file_lock_list) {
struct list_head *btmp;
struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
lock_get_status(q, fl, ++i, "");
move_lock_status(&q, &pos, offset);
if(pos >= offset+length)
goto done;
list_for_each(btmp, &fl->fl_block) {
struct file_lock *bfl = list_entry(btmp,
struct file_lock, fl_block);
lock_get_status(q, bfl, i, " ->");
move_lock_status(&q, &pos, offset);
if(pos >= offset+length)
goto done;
}
}
done:
unlock_kernel();
*start = buffer;
if(q-buffer < length)
return (q-buffer);
return length;
}
/**
* lock_may_read - checks that the region is free of locks
* @inode: the inode that is being read
* @start: the first byte to read
* @len: the number of bytes to read
*
* Emulates Windows locking requirements. Whole-file
* mandatory locks (share modes) can prohibit a read and
* byte-range POSIX locks can prohibit a read if they overlap.
*
* N.B. this function is only ever called
* from knfsd and ownership of locks is never checked.
*/
int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
{
struct file_lock *fl;
int result = 1;
lock_kernel();
for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
if (IS_POSIX(fl)) {
if (fl->fl_type == F_RDLCK)
continue;
if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
continue;
} else if (IS_FLOCK(fl)) {
if (!(fl->fl_type & LOCK_MAND))
continue;
if (fl->fl_type & LOCK_READ)
continue;
} else
continue;
result = 0;
break;
}
unlock_kernel();
return result;
}
EXPORT_SYMBOL(lock_may_read);
/**
* lock_may_write - checks that the region is free of locks
* @inode: the inode that is being written
* @start: the first byte to write
* @len: the number of bytes to write
*
* Emulates Windows locking requirements. Whole-file
* mandatory locks (share modes) can prohibit a write and
* byte-range POSIX locks can prohibit a write if they overlap.
*
* N.B. this function is only ever called
* from knfsd and ownership of locks is never checked.
*/
int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
{
struct file_lock *fl;
int result = 1;
lock_kernel();
for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
if (IS_POSIX(fl)) {
if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
continue;
} else if (IS_FLOCK(fl)) {
if (!(fl->fl_type & LOCK_MAND))
continue;
if (fl->fl_type & LOCK_WRITE)
continue;
} else
continue;
result = 0;
break;
}
unlock_kernel();
return result;
}
EXPORT_SYMBOL(lock_may_write);
static inline void __steal_locks(struct file *file, fl_owner_t from)
{
struct inode *inode = file->f_dentry->d_inode;
struct file_lock *fl = inode->i_flock;
while (fl) {
if (fl->fl_file == file && fl->fl_owner == from)
fl->fl_owner = current->files;
fl = fl->fl_next;
}
}
/* When getting ready for executing a binary, we make sure that current
* has a files_struct on its own. Before dropping the old files_struct,
* we take over ownership of all locks for all file descriptors we own.
* Note that we may accidentally steal a lock for a file that a sibling
* has created since the unshare_files() call.
*/
void steal_locks(fl_owner_t from)
{
struct files_struct *files = current->files;
int i, j;
struct fdtable *fdt;
if (from == files)
return;
lock_kernel();
j = 0;
rcu_read_lock();
fdt = files_fdtable(files);
for (;;) {
unsigned long set;
i = j * __NFDBITS;
if (i >= fdt->max_fdset || i >= fdt->max_fds)
break;
set = fdt->open_fds->fds_bits[j++];
while (set) {
if (set & 1) {
struct file *file = fdt->fd[i];
if (file)
__steal_locks(file, from);
}
i++;
set >>= 1;
}
}
rcu_read_unlock();
unlock_kernel();
}
EXPORT_SYMBOL(steal_locks);
static int __init filelock_init(void)
{
filelock_cache = kmem_cache_create("file_lock_cache",
sizeof(struct file_lock), 0, SLAB_PANIC,
init_once, NULL);
return 0;
}
core_initcall(filelock_init);